Skull melting furnace with removable bottom and process for furnace operation

ABSTRACT

For an improved method of operation, an arc furnace for skull melting refractory materials is constructed with an outer metal shell having upper and lower sections. The lower section may be removed to permit the easy removal of one refractory skull and insertion of another without a prolonged furnace shutdown period.

United States Patent [191 Cichy et al.

[451 Mar. 27, 1973 SKULL MELTING FURNACE WITH REMOVABLE BO'ITOM AND PROCESS FOR FURNACE OPERATION [75] Inventors: Paul Cichy, Buffalo; Robert 0. An-

derson, Akron, both of NY.

[73] Assignee: The Carborundum Niagara Falls, NY.

22 Filed: Dec. 6, 1971 21 Appl. No.: 205,221

Company,

52 US. Cl. ..13/9,l3/35,263/46 51 Int. Cl ..F27d 1/00 58 FieldofSearch ..l3/9,35,1;263/46 [5 6] References Cited UNITED STATES PATENTS 775,654 11/1904 Higgins ..l3/9 1,327,736 1/1920 Reid ..l3/9

Primary ExaminerRoy N. Envall, Jr. Attorney-David E. Dougherty et a].

[ ABSTRACT For an improved method of operation, an arc furnace for skull melting refractory materials is constructed with an outer metal shell having upper and lower sections. The lower section may be removed to-permit the easy removal of one refractory skull and insertion of another without a prolonged furnace shutdown period.

7 Claims, 3 Drawing Figures SKULL MELTING FURNACE WITH REMOVABLE BOTTOM AND PROCESS FOR FURNACE OPERATION BACKGROUND OF THE INVENTION This invention relates to an improved construction and method of operation for electric arc furnaces. This type of furnace is widely used in industry, being especially useful for melting materials of high fusion points, such as refractory oxides or mixtures thereof for the production of fused cast refractory shapes, such as bricks, furnace liners, etc. for high temperature applications. Most of these furnaces are of rather simple design, usually comprising a large cylindrical steel shell, fabricated with a dished bottom closure. The top of the shell is left open for feeding and distributing the charge and to allow the insertion of appropriate electrodes for supplying the arc. For operation, the furnace shell is filled with refractory material and the electrodes lowered to expose this material to the heat of the arc. The electrodes are positioned so that the center part of the charge is melted, but a layer of solid refractory remains between this and the steel shell, insulating and protecting the shell which would otherwise be melted. The molten refractory may be poured out for casting by tilting the furnace. After removal of the molten charge, the furnace is left with a thick lining of refractory material which is called a skull; furnaces of this type are therefore called skull furnaces.

Although the skull shaped refractory layer is essential to prevent destruction of the furnace shell, it presents a difficult problem of removal when the furnace is to be used for melting a different refractory mixture. The furnace must first be cooled and, according to prior art methods, the hard skull layer then be laboriously broken up and shoveled out. Not only is this operation time consuming and difficult, but the furnace shell may be damaged or punctured during the breaking up of the skull material. The purpose of this invention, therefore, is to provide a furnace modification which will permit removal of the refractory skull layer without the need for breaking it up. The invention also provides a method whereby the skull layer may be easily removed for storage and future use, while a second skull layer may be inserted and the furnace put back into service with a minimum of downtime. Further advantages of the invention will become apparent upon reference to the following drawings and detailed description of the invention.

SUMMARY OF THE INVENTION An improved skull furnace for melting refractory materials by an electric arc, the improvement comprising a furnace shell having a lower bottom and an upper mantle for the furnace, said lower bottom being removable, whereby the withdrawal of one fused skull of refractory material from the furnace and the insertion of a second fused skull is facilitated.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sectional side view of a furnace shell and refractory skull lining after furnace shutdown.

FIG. 2 shows a sectional side view of the removable furnace bottom and refractory skull as separated from the upper furnace mantle.

FIG. 3 shows a more detailed sectional side view of the joint between the upper mantle and furnace bottom.

DETAILED DESCRIPTION OF THE INVENTION A sectional side view of the improved furnace of the invention is shown in FIG. 1. This represents the furnace as it would be after the molten change had been poured and the arc electrodes were removed. In previous furnaces, the cylindrical furnace shell and dished bottom have been welded together in one unit, making it necessary to either lift the refractory skull 10 out of the top of the furnace shell or else break up the skull with jack hammers. In the improved furnace shell of the invention, the shell is made in two parts, an upper mantle l2 and a furnace bottom 14. The mantle and bottom are fastened together during furnace operation by bolts passing through the flanges l6 and 17. After shutdown, the flanges are separated and the furnace bottom 14, carrying the refractory skull 10, is lowered on an appropriate lifting device 18 and removed to storage by a conveyor unit 20 (see FIG. 2). Usually the refractory skull will contract sufficiently upon cooling to permit easy separation from the upper furnace mantle 12. This separation may be facilitated by making the upper mantle 12 tapered with a lower part of larger diameter than that of the upper part. After the first skull and furnace bottom has been removed, a second matching furnace bottom can be fastened to the mantle. In a preferred mode of operation, a second skull of different composition, resting upon the second matching furnace bottom, may be inserted in the upper mantle l2 and the mantle and furnace bottom then bolted together as before. The furnace can then be charged and put back into operation, either with or without a preinstalled skull layer. Downtime is thus greatly reduced, compared with previous methods which involve long periods for furnace cooling and require the breaking up and piecemeal removal of the refractory skull layer from the furnace.

In FIG. 3 a detailed side view of the flanged connection between upper mantle l2 and furnace bottom 14 is shown. These parts are fastened together by appropriate bolts 22. Since the furnace walls may be cooled by external streams of liquid (not shown), pipe sleeves 24 are installed around each bolt hole to prevent any leakage of liquid into the furnace through the joint between the two flanges 16 and 17. A gasket of resilient material 26 is installed between the flanges to aid in sealing this joint. The upper flange 16 is also provided with an overhanging circular lip 28 which carries cooling liquid away from the flange joint. With these improvements, therefore, a melting furnace gains much greater versatility in that it can be quickly shifted from one type of refractory to another with a minimum of downtime and labor cost.

Since the mantle and furnace bottom are bolted together during furnace operations, it is apparent that no restrictions are placed on furnace charging and heating procedures. The furnace may be tilted at any angle required for casting the fused refractory without affecting the attachment of the mantle and furnace bottom. The furnace, therefore, differs in thisrespect over those which maintain a vertical position and produce only a solid ingot of fused refractory within the furnace itself.

What is claimed is:

l. A tiltable skull furnace for melting refractory materials by an electric arc and pouring molten material therefrom, the furnace having a shell comprising a furnace bottom bolted to an upper mantle, said furnace bottom being detachable from the upper mantle to permit the removal from the furnace of a solidified skull layer of refractory material, said layer being supported by the detachable furnace bottom.

2. A tiltable skull furnace according to claim 1 in which the upper mantle and furnace bottom are flanged for attachment together during furnace operation.

3. A tiltable skull furnace according to claim 2 in which the upper mantle flange contains an overhanging lip and bolt holes protected against the entry of cooling liquids.

4. A tiltable skull furnace according to claim 2 in which the upper mantle is tapered, having a lower part of larger diameter than that of the upper part.

5. A process for removing fused skulls of refractory material from a tiltable skull furnace according to claim 1, which comprises:

a. cooling the furnace below operating temperature, after casting to solidify the skull of refractory material remaining therein;

b. detaching the furnace bottom from engagement with the upper mantle; and

c. lowering the furnace bottom with the skull of refractory material thereon from within the upper mantle.

6. A process according to claim 5 which further comprises removing the furnace bottom with the skull of solidified refractory material to storage.

7. A process for inserting fused skulls of refractory material into a tiltable skull furnace according to claim 1, which comprises:

a. raising the furnace bottom with a skull of refractory material thereon within the upper mantle; and

b. engaging the furnace bottom with the upper mantle and bolting the two parts together. 

1. A tiltable skull furnace for melting refractory materials by an electric arc and pouring molten material therefrom, the furnace having a shell comprising a furnace bottom bolted to an upper mantle, said furnace bottom being detachable from the upper mantle to permit the removal from the furnace of a solidified skull layer of refractory material, said layer being supported by the detachable furnace bottom.
 2. A tiltable skull furnace according to claim 1 in which the upper mantle and furnace bottom are flanged for attachment together during furnace operation.
 3. A tiltable skull furnace according to claim 2 in which the upper mantle flange contains an overhanging lip and bolt holes protected against the entry of cooling liquids.
 4. A tiltable Skull furnace according to claim 2 in which the upper mantle is tapered, having a lower part of larger diameter than that of the upper part.
 5. A process for removing fused skulls of refractory material from a tiltable skull furnace according to claim 1, which comprises: a. cooling the furnace below operating temperature, after casting to solidify the skull of refractory material remaining therein; b. detaching the furnace bottom from engagement with the upper mantle; and c. lowering the furnace bottom with the skull of refractory material thereon from within the upper mantle.
 6. A process according to claim 5 which further comprises removing the furnace bottom with the skull of solidified refractory material to storage.
 7. A process for inserting fused skulls of refractory material into a tiltable skull furnace according to claim 1, which comprises: a. raising the furnace bottom with a skull of refractory material thereon within the upper mantle; and b. engaging the furnace bottom with the upper mantle and bolting the two parts together. 